1. Field of the Invention
The present invention relates to a refrigeration cycle apparatus provided with a compressor, a use side heat exchanger, a heat source side heat exchanger and an expander, and more particularly to a refrigeration cycle apparatus in which carbon dioxide is employed as a refrigerant constituting a refrigeration cycle.
2. Description of Prior Art
As the refrigeration cycle apparatus provided with the expander, there are, for example, structures described in JP-A-2002-22298 (patent document 1) and JP-A-2001-66006 (patent document 2). In the structure described in the patent document 1, an energy recovered by the expander is used as an auxiliary power of the compressor. Further, in the structure described in the patent document 2, a direction of the refrigerant flowing through the expander is fixed in both of a cooling operation and a heating operation.
In the prior arts mentioned above, since the expander and the compressor are integrally formed, a heat leak from the compressor to the expander is large, so that there is a defect that an efficiency of the refrigeration cycle apparatus is lowered.
Further, in both of the cooling operation and the heating operation in the refrigeration cycle apparatus, it is not considered to keep a pressure difference between the inlet and the outlet of the expander and an amount of the refrigerant flowing through the expander proper. Accordingly, there is a problem that the efficiency is lowered.
There is a case that a two-stage compressor is employed as the compressor, however, this case does not consider a matter that a discharge pressure of a first stage compression portion (a suction pressure of a second stage compression portion) is set to a proper pressure. Accordingly, the efficiency of the compressor may be lowered.
Further, it is not considered to properly control an amount of the refrigerant circulating in the refrigerant cycle. Accordingly, there is a problem that the efficiency of the refrigeration cycle is lowered in the case that the refrigerant circulating amount is improper.